GB790762A — A hydrate of lignocaine hydrochloride and process for making it

USPTO Abstract

The invention comprises diethylaminoacetyl-2:6 - dimethylanilide ("lignocaine") hydrochloride monohydrate in the form of discrete particles and processes for its manufacture by combining lignocaine hydrochloride with sufficient water to form the monohydrate. The manufacture may suitably be carried out by precipitating the monohydrate from an aqueous solution of the hydrochloride by adding a water-miscible organic solvent, or by crystallizing the monohydrate from a solution of the hydrochloride in a solvent consisting of a mixture of water and a water-miscible liquid (e.g. acetone, methyl ethyl ketone or dioxane), or by bringing the hydrochloride into contact with water vapour, e.g. by treating it with humid air, until the hydrochloride has taken up sufficient water to form the monohydrate and which is then recrystallized from a solvent in order to form discrete particles. In examples: (1) lignocaine is dissolved in 33 per cent hydrochloric acid, acetone is added and the monohydrate is crystallized from the solution; (2) lignocaine hydrochloride formed by subjecting a solution of lignocaine in dilute hydrochloric acid to azeotropic distillation with benzene is recrystallized from methyl ethyl ketone containing a small quantity of water, to give the monohydrate and (3) lignocaine hydrochloride is exposed to humid air and the resulting hydrate is recrystallized from methyl ethyl ketone.